Geminal dinitro compounds are precursors for energetic plasticizers used in the manufacture of explosive materials and propellant compositions for defense and industrial applications. For example, 2,2-dinitro-1-propanol (DNPOH) is used in the synthesis of energetic plasticizer compounds, such as bis(dinitropropyl)-acetal (BDNPA) and bis(2,2-dinitropropyl)-acetal/bis(2,2-dinitropropyl)formal (BDNPF). Geminal dinitro compounds may be synthesized from a nitroparaffin starting material. The synthesis of the geminal dinitro compound DNPOH from the nitroparaffin starting material 2-nitroethane involves the following two chemical reactions:CH3CH2NO2+NO2−→CH3CH(NO2)2  (Reaction 1)CH3CH(NO2)2+H2CO→CH3CH(NO2)2CH2OH  (Reaction 2)As shown in Reaction 1, 2-nitroethane is converted to 1,1-dinitroethane by oxidative nitration of the nitro substituted carbon. Condensation of 1,1-dinitroethane with formaldehyde results in the formation of DNPOH, as shown in Reaction 2. Reaction 2 is a well established reaction having yields exceeding 95%.
The oxidative nitration of the nitroparaffin shown in Reaction 1 is an industrially significant reaction in the synthesis of geminal dinitro compounds. One method of forming geminal dinitro compounds is by chemical oxidation of the 2-nitroethane. The oxidizing source for the nitration reaction is conventionally provided by a primary chemical oxidizer. As the primary chemical oxidizer is used during the reaction, a secondary chemical oxidizer is used to regenerate the primary chemical oxidizer to perform additional reactions. Thus, formation of geminal dinitro compounds by chemical oxidation results in a large volume of corrosive, inorganic salt waste. Moreover, the reaction volume is limited by the amount of chemical oxidizer available.
U.S. Pat. No. 2,997,504 to Shechter et al. describes a method of preparing a gem polynitro compound by reacting a nitronate salt and silver or mercury ions. The nitronate salt of a primary or secondary nitroparaffin is reacted with silver nitrate and an inorganic nitrite to produce a geminal dinitro compound and metallic silver.
C. M. Wright and D. R. Levering, “Electrolytic Preparation of Gem-Dinitroparaffins,” Tetrahedron, 19(Suppl. 1):3-15 (1963), describes an electrolytic process for the preparation of geminal dinitroparaffins via electrolytic oxidative substitution of a nitro compound salt using a silver (Ag) mediator as follows:R C—NO2+Ag+→RĊ—NO2+Ag0  (Reaction 3)RĊ—NO2+NO2−→RC—(NO2)2−  (Reaction 4)RC—(NO2)2−+Ag+→RC—(NO2)2+Ag0  (Reaction 5)The silver anode is electrolytically oxidized to generate silver ions which react with nitrite ions and ethylnitronate ions to form 1,1-dinitroethane and silver metal, as shown in Reaction 3. This initial electron transfer creates a radical from the nitroparaffin ion. Nucleophilic attack on this radical by a nitrite ion (NO2−) generates a dinitro-intermediate, such as that shown in Reaction 4. The dinitro-intermediate is oxidized to the geminal dinitro compound, as shown in Reaction 5.
After prolonged electrolysis, the deterioration of the silver anode and precipitation of silver powder in the bottom of the anode compartment was observed. Thus, this electrolytic process may be impractical for industrial use due to the high cost of the silver consumed during the reaction.
Komblum et al., “Oxidative Substitution of Nitroparaffin Salts,” J. Org. Chem, 48:332-337 (1983) describes that α,α-dinitro compounds, α-nitro sulfones, and α-nitro nitriles are obtained when nitroparaffin salts are coupled to nitrite, benzenesulfinate, and cyanide ions by the agency of potassium ferricyanide. The amount of potassium ferrocyanide limits the amount of dinitro compound that may be synthesized.
U.S. Pat. No. 4,910,322 to Grakauskas et al., describes a method for converting nitroalkanes to gem-dinitro compounds using oxidative nitration. An organic nitro compound is reacted with a source of nitrite ions in the presence of a chemical oxidizing agent, such as sodium persulfate (Na2S2O8) and potassium persulfate (K2S208), and a catalytic amount of an alkali metal ferricyanide. The chemical oxidizing agent is consumed during the reaction, adding additional expense and creating substantial waste to the process.
Despite the existence of methods known in the art for chemically synthesizing geminal dinitro compounds, there remains a need in the art for methods that produce substantial yields of geminal dinitro compounds while reducing or eliminating waste and expense. Thus, improved methods of performing oxidative nitration reactions are desirable.